The present invention is related to the field of manufacturing of dental restorations such as crowns, bridges, abutments and implants. When a patient requires a dental restoration the dentist will prepare the teeth e.g. a damage tooth is grinded down to make a preparation where the crown is glued onto. An alternative treatment is to insert implants (titanium screws) into the jaw of the patient and mount crowns or bridges on the implants. After preparing the teeth or inserting an implant the dentist normally makes an impression of the upper jaw, the lower jaw and a bite registration or a single impression in a double-sided tray (also known as triple trays).
The impressions are sent to the dental technicians who actually manufacture the restorations e.g. the bridge. The first step to manufacture the restoration is traditionally to cast the upper and lower dental models from impressions of the upper and the lower jaw, respectively. FIG. 1a and FIG. 8 shows a dental model and a impression, respectively. The models are usually made of gypsum and often aligned in a dental articulator using the bite registration. The articulator simulates the real bite and chewing motion. The dental technician builds up the dental restoration inside the articulator to ensure a nice visual appearance and bite functionality. A proper alignment of the cast in the articulator is crucial for the final restoration.
CAD technology for manufacturing dental restoration is rapidly expanding improving quality, reducing cost and facilitating the possibility to manufacture in attractive materials otherwise not available. The first step in the CAD manufacturing process is to create a 3-dimensional model of the patient's teeth. This is traditionally done by 3D scanning one or both of the dental gypsum models. The 3-dimensional replicas of the teeth are imported into a CAD program, where the entire dental restoration or a bridge substructure is designed. The final restoration 3D design is then manufactured e.g. using a milling machine, 3D printer, rapid prototyping manufacturing or other manufacturing equipment. Accuracy requirements for the dental restorations are very high otherwise the dental restoration will not be visual appealing, fit onto the teeth, could cause pain or cause infections.
In an ideal 3D scanner and dental CAD/CAM solution the dental laboratory or dentist would not need to make a gypsum model from the impression but rather scan the impression directly. This would make the handling easier and less costly. Also the restoration would be more accurate as the impression geometry is more accurate than a sectioned gypsum copy of this. Even if an impression scan could be done with CT or MR scanning equipment such scanners are prohibitively expensive and do not provide the required accuracy. Optical scanners such as laser or white light 3D scanners are on the contrary less costly and provide a higher accuracy and detail level. The problem with optical surface scanners is that these typically cannot efficiently scan the narrow cavities of a dental impression. Typically the scans would lack data or be less accurate in the deep narrow parts of the impression.
An alternative to impression scanners is direct in-the-mouth scanners. However impression scans have a clear number of advantages compared to in-the-mouth scanners including no mandatory equipment investment at dentist clinic, virtually no training for impression taking, shorter chair time, a physical model can always be poured in case of scanning problems or used as physical reference, low accuracy for in the mouth scanners, no powdering of the patient mouth necessary, and significantly reduced difficulties in capturing the antagonist and larger areas and contrary to in-the-mouth scan the impression has the margin line clearly visible.